The present invention relates to a sequence control system, and more particularly, to a system which is designed to check the operation of an information processor during the operation thereof.
In a conventional sequence control system, a desired sequence instruction is read from the sequence program, and the sequence is processed and controlled in its processing circuit. Such a sequence control system has already been disclosed, for example, in U.S. Pat. No. 3,944,987 to Koyanagi et al. Further, a sequence block display system of the kind referred to has been suggested in U.S. Pat. No. 3,964,026 to Yamauchi et al, in which a sequence circuit block is searched in the memory section thereby displaying it.
However, in the known programmable logic controller (PLC), the check of the logic and operation, such as debugging at the side of the processing unit, is performed through a process I/O controller (PIOC). There are known a conventional system, as shown in FIG. 1, in which connection is established between a sequence processing unit 100 (which corresponds to the abovementioned processing unit), a process control section 200 and a production installation 300; and the operation check is made under the condition where the production installation 300 (usually, process system) is in operation. Now, the process control section 200 includes a process I/O controller (PIOC) and a process I/O unit (PI/O). Such a system is characterized in that the operation check is made after the production installation is built, and so, the sequence programs are debugged after the production installation is built.
However, in general, many PLC users tend to desire to build-in the sequencer according to the situation where a new production installation is being built. To this end, if the operation check of the sequence programs can be performed only after the production installation has been built to a certain extent, the system will be low in work efficiency. In addition, debugging requires connection between the process control section and the actually-built production installation. This may damage devices in the production installation and in some cases, may lead to serious injury to the operators.
In order to eliminate the above-mentioned defects, there has been suggested another system shown in FIG. 2 in which a simulation panel is added in place of the production installation. As will be understood from FIG. 2, the production installation in FIG. 1 is replaced by a simulation panel 400 and debugging is carried out within the factory.
The simulation panel 400 is mounted with a multiplicity of (for example, in the order of thousands) switches for setting input data and a multiplicity of (for example, in the order of thousands) lamps for checking the states of outputs, which switches and lamps are associated with process inputs and outputs respectively. Since use of the simulation panel 400 allows debugging to be carried out together with building of the production installation, the work steps are greatly reduced, without the danger of device damage or of serious injury to the operators, as mentioned above.
Nevertheless, this type of system utilizing a simulation panel has defects in that the system is expensive due to the fact that the simulation panel is provided with thousands of switches; and additional complicated wirings (usually, 2000 to 4000) must be completed between the simulation panel and the process I/O unit PI/O, resulting in time-consuming labor and high cost. This is because the above-mentioned system of FIG. 1 requires connection only between the PI/O and the production installation, but in the system of FIG. 2, additional connection must be provided to the simulation panel.
These defects come from the fact that an attempt has been made to check the operation, using a conventional process control section. In other words, an operation check at the side of the sequence processing unit always requires reception of information of the process inputs and transmission of the processed results to process outputs. To realize this, in addition to the above inputs and outputs, an interface between the inputs and outputs and the sequence processing unit must be provided. In the conventional system, a known process control section has been used as such an interface. As a result, the number of wiring points was required. In another point of view, a check at the side of the sequence processing unit is carried out by checking the outputs corresponding to the associated inputs. This means that this method restricts the checking at the sequence processing unit. Further, the application of an input data at an input terminal may cause the output states at output terminals to change. In this case, it is difficult to detect such changes in output states at the output terminals with the above-mentioned sequence panel. Furthermore, it is difficult to cope with a request to provide information relating to the current and previous states of the output terminals. In summary, the above-mentioned systems have a defect in that they do not provide flexibility in performing the logical operation check.